Mites or Spiders on a Holly Tree

Hollies bear vibrant red berries.

Holly trees (Ilex spp.) are low-maintenance evergreen plants often used as specimens or accent trees. Commonly planted species include American holly (Ilex opaca), which grows in U.S. Department of Agriculture plant hardiness zones 5 through 9, and English holly (Ilex aquifolium), a European native that prefers USDA zones 7 through 9. Healthy hollies are associated with few serious potential problems, but spider mites occasionally infest them.

Spider Mites

Spider mites infrequently become serious holly tree pests, particularly the southern red spider mite and the false spider mite, sometimes called the privet mite. These tiny arachnids congregate in large numbers to feed on the undersides of holly leaves. The false spider mite thrives in hot, dry conditions and their populations increase from early summer through early autumn. The southern red spider mite is one of the few cool-weather mites and their populations peak during spring and autumn when the humidity levels remain high.

Symptoms

Small spider mite populations typically don't cause much visible damage, but large numbers can make holly tree foliage look unsightly. These pests feed by piercing the plant tissue with their sucking mouth parts and withdrawing the fluids. This results in a stippling of small, pale yellow dots appearing on the leaves. Affected foliage sometimes turns an unhealthy looking bronze or gray color before dropping from the tree prematurely. Trees sometimes look scorched or appear to have suffered winter injury. If left untreated, severe infestations of southern red spider mites can kill entire trees. Spider mites also spin fine silk webbing that can entirely cover the upper and lower surfaces of leaves as well as the branch tips.

Cultural Control

Because false spider mites thrive in dry, dusty conditions, regularly spray down any dirt roads, pathways or garden areas near your holly tree to remove the dust. Spraying the foliage with a strong jet of water from your garden hose at least twice a week also helps wash the tiny pests from the foliage. Many beneficial insects help keep spider mite populations in check. Natural enemies include predatory mites, ladybugs, thrips, lacewings, minute pirate bugs and bigeyed bugs. You can purchase ladybugs and predatory mites and release them directly on your holly tree to help control spider mite populations.

Chemical Treatments

Insecticidal soap treatments can help reduce spider mite numbers if you spray your tree before their populations get too large. Following the directions on the product's label, mix between 5 and 8 tablespoons of insecticidal soap product into a gallon of water. The soap must make contact with the pests in order to work, so thoroughly cover the tops and undersides of leaves. Repeat applications every seven to 10 days until you achieve control. Don't use insecticidal soap sprays when temperatures soar above 90 degrees Fahrenheit or you risk injuring your tree. Avoid using insecticides containing carbaryl or pyrethroids, because those substances actually increase spider mite populations by stimulating reproduction.